The speaker crossover is a component hidden within just about every loudspeaker. Crossovers are also sometimes also found within amplifiers or receivers, especially home cinema receivers where the subwoofer for bass playback is separate from the satellites. Aside from these specialized technologies, it’s generally true that every loudspeaker with more than one driver in its enclosure requires a crossover.
As its name suggests, a crossover is where the unfiltered audio signal is divided according to a predefined upper or lower threshold. The speaker crossover supplies each driver with the signal range it was designed to best reproduce. For example, crossovers ensure that tweeters only receive the highest frequencies, not any of the lower ones this driver was not designed to reproduce. This makes a crossover something akin to a loudspeaker’s central nervous system.